NEO-ZMC
| |
| Package | SOIC24 |
| Manufacturer | 
|
| First use | 1995 ? |
| Used on | cartridges |
Z80 Memory Controller. Provides a hardwired 32KiB bank and switchable 16, 8, 4, and 2KiB banks arranged as a register file. To save pins, the Z80's upper address lines (A15~A8) are used for data input. The chip's write strobe is port address decoded inside the system.
Pinout
OpenOffice Draw file: File:Neo-zmc.odg
Pins 10, 11, 12 are surely not connected since the addressing scheme doesn't allow mapping over 512KiB.
- SDA0, SDA1, SDA8~15: Z80 address bus
- SDRD0: Decoded write signal from NEO-D0 (latch on rising edge)
Operation
SDA8~15 is used for the bank number (data), SDA0 and SDA1 for selecting the bank zone.
| SDA1 | SDA0 | Z80 port | Bank zone | Address range | Size | Latch size |
|---|---|---|---|---|---|---|
| 0 | 0 | $08 | 0 | $F000~$F7FF | 2KiB | 8 bits |
| 0 | 1 | $09 | 1 | $E000~$EFFF | 4KiB | 7 bits |
| 1 | 0 | $0A | 2 | $C000~$DFFF | 8KiB | 6 bits |
| 1 | 1 | $0B | 3 | $8000~$BFFF | 16KiB | 5 bits |
Details
SDRD0 must be high before configuring banks.
To configure a bank to be accessed (e.g. bank 0 in the $8000~$BFFF range):
- Set SDRD0 low (prepare for new bank configuration, outputs are tri-stated)
- Set SDA0~15 = $8003 (select bank 0 and 16k range size) Why $8003 and not just $0003 ?
- Set SDRD0 high (latch bank, ready to convert inputs to proper output signals)
- Now, when the Z80 reads the $8000~BFFF range, NEO-ZMC will map this to the M1 ROM zone $00000~$03FFF;
To configure a bank to be accessed (e.g. bank 1 in the $8000~$BFFF range):
- Set SDRD0 low (prepare for new bank configuration, outputs are tri-stated)
- Set SDA0~15 = $8103 (select bank 1 and 16k range size) Why $8103 and not just $0103 ?
- Set SDRD0 high (latch bank, ready to convert inputs to proper output signals)
- Now, when the Z80 reads the $8000~BFFF range, NEO-ZMC will map this to the M1 ROM zone $04000~$07FFF;